Recently, demand for enhanced sensitivity and image quality of silver halide light sensitive photographic materials has become stronger. In addition, requirements for enhanced photographic performance which is more resistant under external factors such as pressure, processing fluctuations and storage at high temperature and/or high humidity, have been increased.
In response to such requirements, an attempt to enhance photographic performance of a silver halide emulsion by introducing dislocation lines into silver halide grains was made. JP-A 63-220238 and 1-102547 (herein, the term, JP-A means an unexamined published Japanese Patent Application) disclose techniques for improving photographic characteristics through the introduction of dislocation lines. However, as can be seen from the fact that the disclosure of the techniques described above was followed by disclosure of a number of techniques regarding the dislocation lines, further improved technique of dislocation line introduction is still required.
JP-A 3-175440 discloses a technique of allowing dislocation lines to be concentrated at the edge of tabular grains to improve sensitivity and reciprocity law failure characteristics. JP-A 6-27564 discloses a technique of restricting dislocation lines to fringe portions of tabular grains to improve sensitivity and pressure resistance.
Noticeable results of the prior art include improvements of photographic performance by restricting the position of dislocation lines to a specific site. It is supposed by the inventors of the present invention that restriction of dislocation lines to the specific position also limits the position of deteriorating factors produced along with the dislocation lines and these techniques are restrained so as to not produce influences counteracting improvement effects due to the dislocation lines.
The inventors further noted that introduction of iodide ions accompanied formation of a high iodide layer within the grain. As disclosed in JP-A 6-27564, a means for introducing dislocation lines is to introduce iodide ions, forming a gap or misfit of the crystal lattice.
In a technique regarding an iodide content continuously varying layer disclosed in JP-A 5-53232, 9-138473 and 9-211759, improvement of photographic performance such as sensitivity and pressure resistance were accomplished by reducing the gap and/or misfit of the crystal lattice. However, the gap and/or misfit of the crystal lattice resulting from introducing the dislocation in the prior art, i.e. the presence of a layer in which the iodide content is steeply varied, resulted in possibility of counteracting the effects of the iodide content continuously varying layer described above.
It has not been clarified from the prior study whether the crystal lattice gap/misfit as in the prior art is essentially dispensable or not to introduce the dislocation lines. It is supposed that an excessively high iodide layer may be formed.
The presence of the high iodide containing layer with the grain is contemplated to be related to deterioration of photographic performance, such as sensitivity loss due to closely localized lattice defects, lowered pressure resistance and deterioration in processability due to iodide ions released at development.
Supposing that when dislocation lines are formed according to the prior art, a high iodide layer is also concurrently formed, leading to deterioration in photographic performance due to the high iodide layer as well as improved photographic performance due to the dislocation lines, so that effects of the dislocation lines can not be sufficiently displayed, the inventors of the present invention made further study.